Service frequency ranges are getting extended in the recent communication networks and radiuses of cells are gradually decreased for supporting (covering) high-speed communication and more traffic. Thus, many problems may be caused in view of applying the conventional centralized cellular radio network as it is even later. That is, since a position of the base station is fixed, flexibility of a radio link configuration is low. As a result, it has been difficult to efficiently provide communication services in a radio (wireless) environment where there is a rapid change in traffic distribution and call demands.
To address such problems, a relay, more particularly, a multi-hop relay has been considered in the next generation wireless communication system, called as Long Term Evolution Advanced (LTE-A) system or an Evolved Universal Terrestrial Radio Access (E-UTRA) system. The relay system can broaden cell service coverage by covering a partial shadow area generated within a cell region, increase system capacity, and reduce an initial installation charge since a relay (hereinafter, referred to as ‘relay station (RS)’) is established in an initial stage when a service request is not frequently made.
In the relay system, a relay node (RN) may be applied in two types including a non-transparent type (hereinafter, referred to as “type 1”) and a transparent type (“type 2”).
The type 1 relay node may be able to relay both a control channel and a data channel to a terminal, and perform an initial network entry process, a ranging process and the like, instead of a base station. The type 1 relay node may be generally applied for the purpose of a cell coverage extension, and the type 1 relay system is applied in a distributed form that a line between the relay node and the terminal is controlled directly by the type 1 relay node.
The type 2 relay node may be able to relay only a data channel in a simply amplifying manner. The type 2 relay node may perform a mutually cooperative relaying with the base station to obtain diversity for improving a user data processing rate other than the purpose of the cell coverage extension. Therefore, from the perspective of the terminal, the type 2 relay node may seem to be a part of base station, so it is called as a transparent relay node. The relay system is applied in a centralized form that the line between the relay node and the terminal is controlled directly by the base station.
Meanwhile, the type 2 relay node has no cell ID. Accordingly, the type 2 relay node is unable to transmit reference signals to the terminal such that the terminal can perform channel measurement. Hence, channel estimation efficiency may be deteriorated in the relay system having the type 2 relay node.